1. Field of the Invention
This invention relates to a nonvolatile semiconductor memory device with a stacked gate structure having a floating gate electrode and control gate electrode stacked on a semiconductor substrate and a manufacturing method thereof. Further, this invention relates to a semiconductor device having a gate electrode formed on a semiconductor substrate with a gate insulating film disposed therebetween.
2. Description of the Related Art
Recently, miniaturization of elements is rapidly advanced in an electrically programmable and erasable nonvolatile semiconductor memory (EEPROM). In the EEPROM, high voltage is applied to the control gate electrode in the case of programming. Then, electrons are injected from the substrate side into the floating gate electrode which lies under an inter-poly insulating film via a tunnel insulating film. In the case of erasing, electrons in the floating gate are extracted.
For injection or extraction of electrons with respect to the floating gate, high voltage is required and great stress is applied to the tunnel insulating film formed of an oxide film. As a result, defects called traps are formed in the tunnel insulating film. Therefore, a leak current increases and the data holding characteristic will be deteriorated. The leak current caused by application of the stress depends on the film thickness of the tunnel insulating film to a great extent and the leak current more easily flow as the film thickness becomes smaller. The phenomenon becomes a main factor which prevents the tunnel insulating film from being made thin.
As the measure for solving the above problem, a method for reducing the leak current by introducing nitrogen into the tunnel insulating film to increase the dielectric constant of the tunnel insulating film and increase the physical film thickness is used. In this case, nitrogen is introduced into the tunnel insulating film by annealing a silicon oxide film in ammonium (NH3) gas, nitrogen monoxide (NO) gas or dinitrogen monoxide (N2O) gas. However, in the process using NH3 gas, for example, an after-heat treatment at high temperatures is required to securely maintain the high reliability since a large amount of hydrogen is introduced in the tunnel insulating film. Further, in a process using NO or N2O gas, there occurs a problem which is associated with the reliability and in which a hole trap amount at the stress application time increases (JP-A H1-307272 (KOKAI)).
Further, recently, using an insulating film with a dielectric constant larger than that of a conventional silicon oxide film or silicon oxide-nitride film as an inter-poly insulating film is studied with miniaturization of the nonvolatile semiconductor memory device. However, when an insulating film with the large dielectric constant such as a metal oxide film is sued as the inter-poly insulating film, metal is diffused through the floating gate electrode and further diffused into the tunnel insulating film, thereby causing the reliability of the tunnel insulating film to be deteriorated.